There are a number of instances where Chazal mention 300 barrels of oil or wine:

When measuring and transferring liquids to customers in the marketplace, a residual amount remains in the merchant's utensils. With many customers, this can add up to a large volume. Over the course of Chol HaMoed, Abba Shaul ben Batnis accumulated 300 barrels of residual wine, and his colleagues accumulated 300 barrels of residual oil, which they donated for the public welfare (Beitzah 29a).

Chananya ben Chizkiyah went into an attic and was given 300 barrels of lamp oil. He stayed there until he resolved the seeming discrepancies between the Torah and Sefer Yechezkel (particularly the mystical passage of ma'aseh merkavah). As a result of his toil, the Rabbis were satisfied that there was no need to exclude Sefer Yechezkel from the canon of Tanach (Chagigah 13a; Menachos 45a; Shabbos 13b).

R' Zachai was not always a person of means, but he was always careful to recite kiddush on wine. Once, when he could not afford to buy any wine for Shabbos, his elderly mother sold her kerchief so she could buy him wine. The merit of this mitzvah seems to have changed their fortunes; when she died, she bequeathed him 300 barrels of wine, and when he died he left his children 3,000 barrels of wine (Megillah 27b).

Rabbi Yehudah HaNasi had stomach pains that he cured by drinking 70 year old cider obtained from a non-Jew who owned 300 barrels of it (there was no problem of yayin nesech because wine was presumably not mixed in with the cider). Afterwards, Rabbi gratefully remarked: ברוך המקום שמסר עולמו לשומרים (Avodah Zarah 40b).

Yochanan ben Narbai was a celebrated eater. When he came to the Beis HaMikdash, the azarah cried out: "Raise up your head, O' gates, and let Yochanan ben Narbai student of Pinkai enter and fill his belly with kodshei shamayim!" (The kohanim had to consume a certain quantity of kodshim at the Beis HaMikdash, and that was not always an easy task. The S'fas Emes writes that the azarah praised him because his eating was l'shem shamayim rather than gluttonous). It was said about Yochanan ben Narbai that he would eat 300 calves, drink 300 barrels of wine, and eat 40 seah of pigeons for dessert, although this probably means that his entire household combined consumed that much in one meal (Pesachim 57a). After all, he had many kohanim in his household (Rashi, ibid., sv. Shalosh mei'os).

Rabba bar bar Chana recounted: "One time, we were traveling by ship, and we saw a giant fish with a type of parasite (kilbis) in its nostrils. The sea cast the fish ashore, and it destroyed sixty towns, provided fresh fish meat for another sixty towns, provided salted fish meat for yet another sixty towns, and 300 barrels of oil were filled from just one of its eyes. When we returned twelve months later, we saw that they were crafting beams from its skeleton, and they began to rebuild those destroyed towns." (Bava Basra 73b)

Rabbi Yudan said in the name of Rabbi Ivo[?]: No man leaves this world with half his desires in hand. Rather, if he has one hundred, he wishes to make them two hundred; and if he has two hundred, he wishes to make them four hundred.

It stops there, at four hundred, so if we take it at its word then someone with one hundred whose desires are actually fulfilled will get precisely three hundred more!

300 is a good number!
i automatically think of some lesser know Ssadiqim.

Hhanukh : "after he became the father of Mthushalahh, Hhanukh walked faithfully with God 300 years and had other sons and daughters. Altogether,Hhanukh lived a total of 365 years. Hhanukh walked faithfully with G-d; then he was no more, because G-d took him away." Breshith 5:22-24

Gide3on : "There HaShem told him, “Separate those who lap the water with their tongues as a dog laps from those who kneel down to drink.” 300 of them drank from cupped hands, lapping like dogs. All the rest got down on their knees to drink.
HaShem said to Gide3on, “With the 300 men that lapped I will save you and give the Midianites into your hands. Let all the others go home.” So Gide3on sent the rest of the men of Yisra'el to their tents but kept 300, who took over the provisions and trumpets of the others." Shofttim 7:5-8